Hull form for boats



`lune 17, 1969 c. M. BEST, JR 3,450,090

HULL FORM FOR BOATS Filed March 18, 1968 r l,5o

E INVENT OR 5.25

COE' M. BEST, Ji?.

ATTORNEYS June 17, 1969 c. M. BEST, JR 3,450,090

HULL FORM FOR BOATS Filed March 18,V 1968 ,2

INVENTOR 'C05 M. BEST, JR.

M@ waly fine/fw?,

ATTORNEYS 3,450,090 HULL FORM FOR BOATS Coe M. Best, Jr., 117 Focis St., Metairie, La. 70005 Filed Mar. 18, 1968, Ser. No. 713,627 Int. Cl. H6311 /16; B63b 1/08 US. Cl. 11S-39 8 Claims ABSTRACT 0F THE DISCLOSURE This invention relates to the hull configuration for boats and more particularly to a novel stern construction wherein improved performance characteristics are obtained `and yet wherein a simplified design affords a more economical construction.

This invention applies to propeller driven vessels and although the invention is described in relation to a double screw flat bottom vessel, it is not to be considered as limited to such specific showing as the teachings of this invention are applicable to many types of ywater driven craft. In many boats, in the development of higher power, it has become a common expedient in order to obtain satisfactory propulsive efficiency, to use propellers of larger diameter, This causes the tip of the propeller to be located higher relative to the water line Iand in some cases, above the water line. A result is that air is drawn into the propellers, sometimes causing excessive Nibration and at least causing some cavitation effects where in collapsing air bubbles form a partial vacuum and reduce the thrust of the propeller.

On some conventional boats wherein a at bottom hull is required for low draft purposes it has been common in the past to reduce the propeller diameter so as to maintain the propeller beneath the stern `and yet above the base line of the vessel. This often results in reduced efiiciency, in towboats in particular, and increases the possibility that air will come in from the side of the boat especially in restricted seaways and the like to cause cavitation effects. Additionally, in such a construction a small section modulus of hull girder will be realized just forward of the propellers thereby limiting the capacity of the vessel and reducing the strength of the stern section.

In fiat bottom vessels, it has become common in the art in order to allow an increase in the diameter of the propeller and still retain an adequate size of stern section, to create a tunnel-like configuration for the bottom surface of the hull. Thus, as Iwater is drawn along the bottom of the ship, it will be directed in an upward direction to completely submerge the propeller of the Vessel, thereby utilizing the complete available area of the propeller.

This invention relates to yan improvement in the bottom configuration of the hull wherein a more efiicient tunnel design is realized and additional other advantages are obtained.

There-fore, an object of this invention is to increase the propulsive thrust of the propellers by `altering the configuration of the hull in the addition of an appendage at the sides of the hull.

Another object o-f this invention is to provide increased displacement of the hull for a vessel of a particular capacity.

A further object of this invention is to provide an im- Stats Patent O 3,450,090 Patented June 17, 1969 proved hull configuration which prevents air from entering into the propellers from the sides of the vessel and causing propeller cavitation.

Still another object of this invention is to increase the strength of the hull by increasing the depth of the aft portion of the hull.

A still further object of this invention is to provide a novel hull construction which requires a combination of only flat plate and simple curve surfaces which simplifies the design and reduces the cost of the construction.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described land particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in -which the principle of the invention may be employed.

In said annexed drawings:

FIG. l is a perspective view of the stern section of the hull of a twin screw vessel embodying the principles of this invention;

FIG. 2 is a plan view of a portion of the stern section of the hull of such a twin screw vessel;

FIG. 3 is an elevational view of a portion of the stern section of the hull of the vessel shown in FIG. 2;

FIG. 4 is a transverse section of the hull, at the propeller line, of the twin screw vessel taken along the lines 4-4 of FIG. 3; and

FIG. 5 is a transverse section of the hull, at the propeller line, of a single screw vessel utilizing the principles of this invention.

Referring now to FIG. 1, a portion of the hull 10 of a twin screw vessel embodying the teachings of this invention is shown whereby the relationship between the hull 10, the tunnels 12, 14 the propellers 16, 18 and the water line 20 may be visualized. Although this description is given in reference to a twin screw vessel the teachings of this invention are applicable as -well to single or multiple screw vessels as will be pointed out in greater detail hereinafter. In vessels of this type, it is common to locate the propellers 16, 18 in an elevated position in relation to the hull 10 of the vessel so as to reduce the draft of the vessel to alleviate clearance problems in inland waterways, locks and the like. Such elevation of the propeller 16, 18 necessitates a corresponding elevation of the stern bottom plates in order to provide adequate clearance for the propellers 16, 18, and this transition in elevation in part forms the longitudinally extending tunnels 12, 14. Aft of the propellers 16, 18 the stern bottom plates curve downward to intersect with the essentially vertical transom plate 23 at an elevation below the water line 20, to complete the extent of the tunnels 12, 14. It is common in these vessels that a portion of the propellers 16, 18 may be above the normal water line 20 and it has been the expedient in the past to so design the bottom configuration of the hull 10 to provide tunnels 12, 14 which effect a water iiow over the complete Iarea of the propellers 16, 18 and a more efiicient operation. The advantage of the tunnel arrangement is clearly seen in FIG. 3 where it is noted that the diameter of the propeller 16 would be severely restricted if it were limited between the lowest point of the stern 22 and the extended base line 2S of the vessel.

However, one of the problems involved in this type of hull configuration is that unless a sufficient supply of water is atforded to the propellers 16, 18 under certain conditions of operation as, for example, the various speeds of the vessel, or operation in restricted waterways such as in seaways and the like, there is a tendency for air to come in from the sides of the hull to cause the propellers 16, 18 to cavitate, thereby reducing the eiciency of the propellers. The teachings of this invention apply to streamlining the configuration of the hull 10 of the vessel and particularly to adding appendages 26, 28 to the outer portions of the hull 10 to direct the flow of water in the tunnels 12, 14 `and to eliminate the effects of cavitation.

Referring now to FIG. 4, it may be seen that the bottom configuration of this vessel consists of the combination of longitudinally extending cylindrical surfaces together with a plurality of intersecting plates which may be at or formed of flat plates which are shaped into simple curves. The outer portions of the hull 10 as viewed in FIG. 4 comprise the appendages 26, 28 which form a portion of the tunnels 12, 14. In cross section, it may be visualized that the appendages 26, 2S consist of a combination of circular and linear curves Iat any cross section along their longitudinal extent, the cross section of FIG. 4 being taken at the propeller line of the vessel. The circular curves 30, 32 are portions of cylindrical surfaces 34, 36 extending longitudinally of the vessel, the surfaces 34, 36 having centerlines 34a, 36a which are angled generally inwardly and upwardly to streamline the stern 22 of the vessel and to form the tunnel coniigurations. As seen in FIGS. 2 and 3, the location of the cylindrical sur-face 34 may be determined by reference to the centerline 34a 4and the straight line 38 forming the prole of the lowermost portion of the cylindrical surface 34. A second line 39 depicts the center line of the bilge radius of the vessel, the bilge 40 forming the curved portion between the bottom 41 and the vertical sides 42 of the forward section of the hull.

Referring to FIG. 2 at a point aft of the middle section of the vessel, where the appendage 26 is located line 34a departs from line 39 `at an angle 44 of approximately 10 in ai rearward and inward direction. The angle 44 between lines 34a and 39 is shown as only one embodiment of this invention and in fact, angle 44 may vary from lapproximately 315 and depends on the design and speed of the vessel. Appendage 28, on the opposite side of the vessel and forming the tunnel 14, is similarly inwardly sloped as indicated by cylindrical surface 36 and centerline 36a. The inward slope of appendages 26, 28 provides a streamlining effect for the stern 22 of the vessel to reduce the turbulence of the water behind the vessel and to assist in directing the ow of water into the area of the tunnels 12, 14.

Referring now to FIG. 3, line 3S depicting the bottom of the appendage 26 is shown in elevation in relation to a dashed line 46 which is `an arbitrary horizontal line approximately parallel to the surface of the water and the base line 25 of the vessel. Line 38 departs from line46 in an upward vertical direction at an angle 48 of approximately 10" and this angle 48 also may vary from between 3-15 depending on the design and speed of the vessel. Thus, if the vessel is intended to be used primarily for transportation where relatively fast speeds are employed and where maximum eiciency is desired at such speed, then'the angle between lines 38 and 46 will be shallower and less deflection of the water will be required in order to completely immerse the propeller 16 for optimum eicient use of the screw.

It is apparent that the angle 48 of elevation of line 38 in the vertical plane affects the elevation of the hull 10 at the stern 22 of the vessel and it is clear affects the -height of the tunnel 12 for the ow of water through the propeller 16. Since line 38 is the bottom-center of the cylindrical member 34 forming la portion of the appendage 26 of the hull 10, it will be observed that such cylindrical member 34 will lie generally in an inwardly sloping direction with relation to the side 42 of the vessel and in an upwardly sloping direction in relation to the bottom 41 of the vessel or to the surface of the water.

The cylindrical member 34 may be formed at al constant radius thereby depicting one embodiment of this invention. However, the principles of this invention apply as well if the radius of curvature of this member varies from front to back of the vessel and in fact, such member may take the configuration of a cone having a virtual apex located aft of the vessel. The signiiicance of such cylindrical or conical member is that the member may be readily formed by rolling a at piece of material in 'a single direction which provides a substantial improvement over prior art hull designs which often employ a complex bending of a flat plate.

The usual hull 10 conguration of `a flat bottom lvessel consists of a keel section 50 which is essentially horizontal as seen in cross-section in FIG. 4, extending a short distance on either side of the center line 52 of the vessel. Such keel section 50 is longitudinally vertically elevated in the aft portion of the vessel and slopes from a point amidship to provide lan elevated stern 22 for the vessel.

The keel section 50 intersects, on either side of the centerline 52 of the vessel, with angularly disposed plate portions 54 forming the inner sides of the tunnels 12, 14. The plate portions 54 may be formed of at plates twisted in a simple curve in a longitudinal direction or may be built up of smaller welded plates and they extend essentially horizontally near the center of the vessel, blending into the plane of the at bottom 41 of the vessel. Toward the stern 22 of the vessel the plate portions 54 intersect with the keel section 50 at an angle, reaching a maximum near the location of the propellers 16, 18.

The tops 56 of the tunnels 12, 14 are also formed of at plates which laterally, are horizontally disposed but inclined longitudinally from a blend with the at bottom 41 near the middle of the vessel to a maximum elevation at the propellers 16, 18 and then inclined downwardly to an intersection with the vertical transom plate 23 forming the stern 22 of the vessel. As may be seen in FIGURES 1 and 3, the lower portion of the stern 22 and transom plate 23 and thus the rearwardmost portion of the tunnels 12, 14 are located beneath the water line 20.

As seen in FIGURE 2, the tops 56 of the tunnels 12, 14 intersect with the plate portions 54 on the inner sides of the tunnels in essentially straight longitudinal lines 58 even though the tops 56 of the tunnels form a ramp-like configuration. The outer sides of the vtops 56 intersect with the bilge 40 near the middle of the ship and with the appendages 26, 2S near the stern 22.

The appendages 26, 28 each further include a flat plate 60 disposed for a distance between the cylindrical members 34, 36 and the tops 56 of the tunnels 12, 14, each plate `60 tangentially intersecting the cylindrical members 34, 36 and angularly intersecting the tops 56 of the tunnels 12, 14 at approximately Ztl-40, to form a part of the outer portion of the tunnels.

Although some variation is possible in the configuration of the tunnel and appendage design, it is preferable to maintain such dimensions as to allow the appendage to shroud between l0-50% of the diameter of the propellers 16, 18 for the most effective results. This shroud etect is best seen in the elevational View of FIG. 3 where the appendage 26 obscures the View of the upper portion of the propeller 16.

As pointed out previously, the principles of this invention are applicable as well to single or multiple screw vessels, the showing in FIGURE 5 describing in particular, a single screw Vessel `62. Here is a cross-sectional view is taken at the propeller line to show that a similar tunnel 64 and appendage 66 configuration may be realized. The appendages 66 are again formed of cylindrical or conical sections. However, here the appendages 66 form both sides of the tunnel 64 in which the propeller 68 is located and intersect with a horizontal plate 70, curved in the longitudinal direction to form the top of the tunnel 64. The cylindrical sections are again angled inwardly and upwardly to achieve the preferred tunnel configuration in a manner similar to that previously described for the dual-screw vessel.

The tunnel and appendage configuration of this invention for all embodiments allows water to fiow to the propellers primarily from the sides of the vessel and not from the bow thereby increasing the stability and controllability of the vessel. Further, the construction increases the depth of the vessel at the sides thereby decreasing the draft and protecting the propellers from floating objects or from drawing nets and the like into the screws. Still further this configuration allows the engine 72 and propeller to be mounted horizontally and still maintain eicient operation of the screw, thereby further reducing the cost of the construction.

Other modes of applying the principles of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

I, therefore, particularly point out and distinctly claim as my invention:

1. A hull configuration for a ship for shrouding and directing the flow of water to the propeller comprising a tunnel extending longitudinally of the ship, originating at a location near the middle of the hull, increasing in elevation to a maximum near the stern at the propeller location and decreasing in elevation to the stern of the ship, the tunnel being formed of plate sections curved at most in a single direction and comprising a flat transverse top surface and an appendage depending from the top surface to form the outer portion of the tunnel, the appendage comprising a simple curve surface, and a flat plate member which intersects the top surface.

2. A ships hull configuration as set forth in claim 1 wherein the appendage comprises a cylindrical surface, the flat plate being located between the cylindrical surface and the top surface, tangentially intersecting the cylindrical surface and angularly intersecting the top surface.

3. A ships hull configuration as set forth in claim 1 wherein the appendage comprises a conical surface having a virtual apex located behind the stern of the ship, the at plate tangentially intersecting the conical surface and angularly intersecting the top surface.

4. In the hull of a ship having a tunnel configuration for shrouding and directing water ow to the propeller wherein the tunnel extends longitudinally of the ship, being of a ramp configuration having a planar top surface and being curved in the longitudinal direction from a 10- cation near the middle of the ship to a maximum elevation at the propeller screw, the improvement comprising an appendage depending from the top surface of the tunnel at the outer portion thereof for shrouding a portion of the propeller diameter, the appendage comprising the combination of a generally longitudinally extending simple curved surface and a plate section, the curved surface being tangent with the sides of the ship at the outer portion and with the plate within the tunnel, the plate angularly intersecting the top surface of the tunnel.

5. The improvement as set forth in claim 4 wherein the appendage depends from the top surface of the tunnel a distance to shroud between 10-50% of the diameter of the propeller.

6. A generally flat-bottomed ships hull having a longitudinal recess in its underside extending toward the stern and a propeller mounted within the recess for increased propulsive effectiveness, characterized by gradually increasing height of the recess toward the stern of said hull with the height gradually decreasing substantially for a short distance closely adjacent the stern, the propeller being located within the recess in a region of substantially greatest height of the latter, and the outer sides of the recess being formed by a ridge of downwardly convex cross-section.

7. The hull of claim 6, further characterized by the provision of two longitudinal recesses parallel to each other, with a propeller in each recess, and a longitudinally extending downwardly projecting ridge therebetween, the recesses originating in the after portion of the hull and being defined by transversely flat hull surfaces except for the curved ridges at their outer sides.

8. The hull of claim `6, wherein the ridges at the outer sides of the recess taper toward the respective outer sides of the hull in a forward direction.

References Cited FOREIGN PATENTS 24,741 12/ 1894 Great Britain. 896,775 11/ 1953 Germany.

ANDREW H. FAR-RELL, Primary Examiner.

U.S. Cl. X.R. 114-62 

